This invention relates to a method for determining cure and/or detecting oxidation of spin-on dielectric polymers.
The microelectronics fabrication industry is moving toward smaller geometries in its devices to enable lower power and faster speeds. As the conductor lines become finer and more closely packed, the requirements of the dielectrics between such conductors become more stringent. One class of materials being examined as a replacement for the standard dielectric material, silicon dioxide, is spin-on dielectric (SOD) polymers.
Unlike the traditional silicon dioxide dielectric layers, these dielectric layers are formed by applying a solution containing the oligomeric precursor to the dielectric polymer, spinning to evenly coat and to remove solvent, followed by curing of the polymer. Curing typically occurs by heating the coated substrate to initiate additional polymerization reaction and/or cross-linking. Achieving an adequate degree of cure is essential to minimizing change in mechanical or other properties later on during fabrication or even during use of a device having a SOD polymer. An undesirable oxidation reaction may also occur if cure conditions (such as exposure to oxygen or other oxidants) are not adequately controlled. Detection of such oxidation reactions may also be important to assuring quality control.
Fluorescence has been taught to measure cure, potentially in-situ, of various polymers with the addition of a fluorescent probe (see, e.g., U.S. Pat. No. 5,100,802 and WO86/07456). However, the addition of a probe molecule would be undesirable due to the need for purity and due to high processing temperatures in the microelectronics fabrication process. Intrinsic fluorescence has also been taught as a method for monitoring cure in polyurethanes, (see, e.g., Sun, et al., xe2x80x9cIntrinsic Fluorescence Cure Sensor for Reaction Monitoring in Polyurethane,xe2x80x9d Polymer Preprints, Vol. 35, No. 1, page 435, March 1994, and in polyester/styrene polymers (see, e.g., Grunden, et al., xe2x80x9cCure Monitoring of Styrene Containing Polymer Using UV-Reflection and Fluorescence Spectroscopies,xe2x80x9d Polymer Preprints, Vol. 37, No. 1, March, 1996). However, it was unknown whether SOD polymers possessed this characteristic.
Various analysis methods have been examined to determine cure and oxidation of SOD polymers. FT-Raman analysis can be used to monitor cure of extent of cure, but this method is destructive to the sample. Refractive index may also provide some indication of cure, but it is not very sensitive to oxidation. FT-IR analysis can be used to detect oxidation but is ineffective at detecting cure of important SOD polymers.
Therefore, a need remains for an efficient and cost-effective manner for detecting extent of cure and/or oxidation for spin-on dielectrics.
The Applicants have discovered a method that not only enables monitoring on-line of SOD for extent of cure but would also allow for simultaneous examination for oxidation. Thus, this invention is a method comprising
preparing a sample by coating a thin film of a precursor material, which is free of fluorescent probe molecules onto a substrate and subjecting the precursor material to conditions to attempt to cause cure of the precursor to an organic, aromatic, polymer having a dielectric constant of less than 3.0,
exposing the sample to radiation having a wavelength in the range of 200 to 500 nm,
detecting a resulting emission of radiation, and comparing the emission to the emission for a known cured, non-oxidized standard for the polymer.